Method of detecting recovery from fault in a data transmission system which effects loopback control

Abstract

A looped data transmission system has a pair of looped transmission lines forming two transmission systems having different transmission directions, and a plurality of stations including at least one control station connected to said transmission lines of the two transmission systems. If a fault occurs in the two transmission lines of the two transmission systems in the same section, a loopback configuration is established such that stations adjacent to the faulty section send signals from one system back to the other system. With the loopback configuration being established, the stations which have received supervisory signals sent from a loopback end station send them back to the transmission line of the other system. When one of the loopback end stations has received a supervisory signal from the direction of the faulty section, it is judged that a portion of the faulty section is recovered, and the result of the judgement is communicated to the control station.

What is claimed is: 
     
       1. A method of detecting recovery of a fault in a looped data transmission system comprising two looped transmission lines, the transmission directions of which are opposite relative to each other, and a plurality of stations including at least one control station connected to said transmission lines in such a way that said two looped transmission lines are divided into a plurality of sections by said stations, said method comprising the steps of establishing a loopback configuration between the two transmission lines in a pair of stations such that stations adjacent to a faulty section send signals from one transmission line to the other transmission line in case a fault occurs in the adjacent section; sending supervisory signals from each of the stations adjacent to a faulty section toward the other station via the adjacent faulty section on a respective one of said transmission lines; in case that faults occur in two sections which are not adjacent to each other, controlling the stations positioned between said two faulty sections to effect loopback of any supervisory signals received thereby on one transmission line as well as re-transmission of the received supervisory signal on the same one transmission line to the next adjacent station in the direction of transmission on said one transmission line; judging that a faulty section has recovered from the fault when at least one of said stations adjacent to the previously faulty section receives a supervisory signal via the previously faulty section from an adjacent station; sending a search command signal periodically from the control station to the stations adjacent to a faulty section to inquire whether the faulty section has recovered; and sending from the stations adjacent a faulty section that have received a supervisory signal a recover answer signal to the control station in response to the search command signal. 
     
     
       2. A method according to claim 1, further comprising the step of reconfiguring the loopback condition of a station adjacent a previously faulty section when the control station receives said recovery answer signal from that station.